The disclosures of Japanese Patent Applications Nos. 2000-350771 filed on Nov. 17, 2000 and 2000-200798 filed on July 3, each including the specification, drawings and abstract are incorporated herein by reference in their entirety.
1. Field of the Invention
The invention relates to an art for generating a hydrogen-rich fuel gas by hydrolyzing or pyrolyzing a metal hydride.
2. Description of the Related Art
System constructions for operating fuel cells are roughly divided into a type of construction in which a hydrogen gas accumulated in a tank and so on is supplied to an anode (hydrogen electrode), and a type of construction in which hydrogen produced from a predetermined raw material through a chemical reaction is supplied. As an example of the latter type, a construction that uses a metal hydride, generally termed chemical hydride, is known.
Chemical hydrides are compounds of hydrogen and alkali metals or complex metals, and have a property of producing hydrogen when hydrolyzed or pyrolyzed. The chemical hydrides are also known as substances of very high energy density. Due to recent researches, various metal hydrides, such as NaH, NaBH4, NaAlH4, LiAlH4, LiBH4, LiH, CaH2, AlH3, MgH2, etc., have become known as chemical hydrides.
For example, NaBH4 is known to produce hydrogen and a metal-containing product NaBO2 when hydrolyzed as in the following equation.
NaBH4+2H2Oxe2x86x92NaBO2+4H2
An example of the hydrogen generating apparatus that uses a metal hydride is an apparatus described in Japanese Patent Application Laid-Open No. SHO 54-127891. This apparatus hydrolyzes a metal hydride to generate hydrogen by supplying water to a vessel containing the metal hydride via a water supply pipe provided in the vessel.
A system in which a metal hydride is hydrolyzed needs a water tank for separately storing water to be supplied, and therefore is large in size. A system in which a metal hydride is pyrolyzed consumes energy for heating, and therefore has low energy efficiency.
Therefore, in order to improve the practicability of a fuel gas generation system that uses a metal hydride, the following improvements are demanded. Firstly, a size reduction and an energy efficiency improvement of the system are demanded. In recent years, in particular, installation of fuel cells in vehicles or other moving bodies is being considered. For installation in a moving body, a system of reduced size and improved energy efficiency is strongly demanded. Furthermore, in some cases in the hydrolysis of a metal hydride, the reaction stops at the time of about 50% decomposition because the metal hydride becomes coated with a metal-containing product. Therefore, the second demand is to improve the reaction rate for efficient generation of hydrogen.
It has also been found that due to the presence of impurities, a hydrogen gas generated through decomposition of a metal hydride, in some cases, is not appropriate to be supplied to a fuel cell unless it is further processed.
Furthermore, a metal hydride is consumed as hydrogen is generated. Therefore, the third demand is to establish a method for easily adding a metal hydride.
Accordingly, it is one object of the invention to improve the practicability of a fuel gas generation system that uses a chemical hydride.
In accordance with the invention, a first aspect of a fuel gas generation system for generating a hydrogen-rich fuel gas for a fuel cell includes a reaction portion that generates hydrogen by at least one reaction mode of a hydrolysis and a pyrolysis of a metal hydride, and a supply mechanism that supplies the reaction portion with at least one of a water and a heat that are generated by the fuel cell, in accordance with the reaction mode in the reaction portion.
As for the metal hydride, it is possible to use various substances that hydrolyze or pyrolyze to generate hydrogen, including the aforementioned substances, such as NaBH4 and NaAlH4. This construction makes it possible to use water or heat generated by the fuel cell for the decomposing reaction. In a system in which a hydrolysis is conducted in the reaction portion, the reaction portion is supplied with water generated by the fuel cell. In a system in which a pyrolysis is conducted in the reaction portion, the reaction portion is supplied with heat. By using water or heat generated by the fuel cell in this manner, it becomes possible to omit a water tank for the hydrolysis or an energy source for the pyrolysis or to sufficiently reduce the size thereof. Thus, the entire system can be reduced in size.
A second aspect of the invention includes an exothermic reaction portion that generates hydrogen by an exothermic reaction in which a first metal hydride is hydrolyzed, an endothermic reaction portion that generates hydrogen by pyrolyzing a second metal hydride, and a heat supplying mechanism that supplies a heat generated by the exothermic reaction portion to the endothermic reaction portion. The second aspect and the first aspect have objects to be achieved in common. That is, the second aspect is also intended to improve the energy efficiency in generation of hydrogen, and to reduce the size of the apparatus.
According to the second aspect, hydrogen can also be generated by the endothermic reaction portion utilizing heat generated by the exothermic reaction portion, so that the entire system can be reduced in size and can be made more efficient. Since hydrogen is generated by the endothermic reaction portion as well, the amount of hydrogen that needs to be generated by the exothermic reaction portion can be reduced, and the amount of water that needs to be supplied for the hydrolysis can also be reduced. As a result, there is another advantage of allowing a reduced capacity of the water tank.
A third aspect of the invention includes a metal ion removing mechanism that removes at least a metal ion from a gas generated by hydrolyzing or pyrolyzing a metal hydride in a reaction portion. It is possible to apply the reactor to any one of the reactors in the first aspect and the second aspect, and the reactor portion in the conventional art.
In the decomposing reaction of the metal hydride, a metal-containing product is generated concurrently with hydrogen. The metal-containing product dissolves into water to form metal ions although the amount is small. Metal ions are known to adversely affect fuel cells.
A fourth aspect of the invention includes a passage through which a mixed liquid of water and a metal hydride passes, and a catalyst that is supported in the passage and that accelerates the hydrolysis of the metal hydride. It is possible to apply the reactor to any one of the reactors in the first aspect and the second aspect, and the reactor portion in the conventional art.
Regardless of whether any one of the first to fourth aspect is adopted, it is necessary to appropriately add a metal hydride as a material in a fuel gas generation system for generating hydrogen by hydrolyzing the metal hydride. This addition of the metal hydride can easily be accomplished by using a material cassette as described below. A material cassette in accordance with the invention includes a connecting opening portion, a first storage portion, a second storage portion, a piping structure, and a housing case that houses therein at least the first storage portion, the second storage portion, and the piping structure. The connecting opening portion is a mechanism connected to a piping that communicates with a reactor of a fuel gas generation system. The first storage portion stores a metal hydride. The second storage portion stores water to be used in the hydrolysis.